Generally, ozone gas is generated by feeding oxygen gas from an oxygen-gas cylinder or separated from the air to an ozone generator. However, even if the ozone gas is generated by using the oxygen gas from the oxygen-gas cylinder, the thus obtained ozone gas exists in the oxygen gas with only a concentration of about 5 vol % to 10 vol %. Further, since the ozone gas is strong in self-decomposability, the ozone gas self-decomposes while it is passing through an ozone-gas supply route. At a stage where it is supplied to an ozone-gas consumption equipment, it has a property that its concentration becomes much lower and besides the supply-concentration is unstable. Recently, in the semi-conductor production field, to make use of the oxidation activity of the ozone is increasing for forming an oxidation film on a substrate or the like. In this case, it is desired to supply ozone gas of a stable middle concentration so as to stably produce an oxidation film of an appropriate thickness within a short period of time.
Then the present Applicant's previous proposal was to condense and purify ozone gas by supplying to an adsorbing cylinder filled with an ozone adsorbent, ozone-oxygen mixture gas from an ozone generator (see Patent Literature 1).    Patent Literature: Patent Application Laid-Open No. 2003-171104